Hyperthermia treatment and probe therefor

ABSTRACT

In vivo hyperthermia treatment of a target tissue can include imaging the target tissue with a magnetic resonance imaging (MRI) system, positioning a hyperthermia treatment probe in or proximate to the target tissue based on the imaging, and heating the target tissue by the probe. During the heating, changes in temperature of a volume of tissue that includes the target tissue can be monitored with the MRI system to determine an amount of the heating applied to the target tissue, and the heating can be terminated when the amount of the heating reaches a predetermined amount.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. application Ser. No. 13/601,134, filedAug. 31, 2012, which is a continuation of U.S. application Ser. No.11/957,876, filed Dec. 17, 2007, now U.S. Pat. No. 8,256,430, which is adivisional of U.S. application Ser. No. 10/701,834, filed Nov. 5, 2003,now U.S. Pat. No. 7,344,529, which is a continuation-in-part of U.S.application Ser. No. 10/014,846, filed Dec. 14, 2001, now U.S. Pat. No.7,167,741, the entire contents of each of which is incorporated hereinby reference, and which is a continuation-in-part of InternationalApplication No. PCT/CA01/00905, filed Jun. 15, 2001, which claimspriority to U.S. application Ser. No. 09/593,699, filed Jun. 15, 2000,now U.S. Pat. No. 6,418,337.

BACKGROUND OF THE INVENTION

The treatment of tumors by hyperthermia is known. In one known process,tumors and other lesions to be treated can be heated above apredetermined temperature of the order of 55 C so as to coagulate theportion of tissue heated. The temperature range is preferably of theorder of 55 to 65 C and does not reach temperatures that can causecarbonization or ablation of the tissue.

One technique for effecting the heating is to insert into the lesionconcerned an optical fiber, which has at its inserted end an elementthat redirects laser light from an exterior source in a directiongenerally at right angles to the length of the fiber. The energy fromthe laser thus extends into the tissue surrounding the end or tip andeffects heating. The energy is directed in a beam confined to arelatively shallow angle so that, as the fiber is rotated, the beam alsorotates around the axis of the fiber to effect heating of differentparts of the lesion at positions around the fiber. The fiber can thus bemoved longitudinally and rotated to effect heating of the lesion overthe full volume of the lesion with the intention of heating the lesionto the required temperature without significantly affecting tissuesurrounding the lesion. We define the term “lesion” as used herein tomean any pathologic change in the tissue or organs of a mammaliansubject including, but not limited to, tumors, aortic or otheraneurysms, artery and vein malformations such as thrombosis,hemorrhages, and embolisms.

At this time the fiber is controlled and manipulated by a surgeon withlittle or no guidance apart from the knowledge of the surgeon of theanatomy of the patient and the location of the lesion. It is difficulttherefore for the surgeon to effect a controlled heating which heats theentire lesion while minimizing damage to surrounding tissue.

It is of course well known that the location of tumors and other lesionsto be excised can be determined by imaging using a magnetic resonanceimaging system. The imaging system thus generates for the surgeon alocation of the lesion to be excised but there is no system availablewhich allows the surgeon to use the imaging system to control theheating effect. In most cases it is necessary to remove the patient fromthe imaging system before the treatment commences and that movementtogether with the partial excision or coagulation of some of the tissuecan significantly change the location of the lesion to be excised thuseliminating any possibility for controlled accuracy.

It is also known that magnetic resonance imaging systems can be used bymodification of the imaging sequences to determine the temperature oftissue within the image and to determine changes in that temperatureover time.

U.S. Pat. No. 4,914,608 (LeBiahan) assigned to U.S. Department of Healthand Human Services issued Apr. 3, 1990 discloses a method fordetermining temperature in tissue.

U.S. Pat. No. 5,284,144 (Delannoy) also assigned to U.S. Department ofHealth and Human Services and issued Feb. 8, 1994 discloses an apparatusfor hyperthermia treatment of cancer in which an external non-invasiveheating system is mounted within the coil of a magnetic resonanceimaging system. The disclosure is speculative and relates to initialexperimentation concerning the viability of MRI measurement oftemperature in conjunction with an external heating system. Thedisclosure of the patent has not led to a commercially viablehyperthermic treatment system.

U.S. Pat. Nos. 5,368,031 and 5,291,890 assigned to General Electricrelate to an MRI controlled heating system in which a point source ofheat generates a predetermined heat distribution which is then monitoredto ensure that the actual heat distribution follows the predicted heatdistribution to obtain an overall heating of the area to be heated.Again this patented arrangement has not led to a commercially viablehyperthermia surgical system.

An earlier U.S. Pat. No. 4,671,254 (Fair) assigned to Memorial Hospitalfor Cancer and Allied Diseases and issued Jun. 9, 1987 discloses amethod for a non surgical treatment of tumors in which the tumor issubjected to shock waves. This does not use a monitoring system tomonitor and control the effect.

U.S. Pat. No. 5,823,941 (Shaunnessey) not assigned issued Oct. 20, 1998discloses a specially modified endoscope which designed to support anoptical fiber which emits light energy and is moved longitudinally androtates angularly about its axis to direct the energy. The device isused for excising tumors and the energy is arranged to be sufficient toeffect vaporization of the tissue to be excised with the gas thus formedbeing removed by suction through the endoscope. An image of the tumor isobtained by MRI and this is used to program a path of movement of thefiber to be taken during the operation. There is no feedback during theprocedure to control the movement and the operation is wholly dependentupon the initial analysis. This arrangement has not achieved commercialor medical success.

U.S. Pat. No. 5,454,807 (Lennox) assigned to Boston ScientificCorporation issued Oct. 3, 1995 discloses a device for use inirradiating a tumor with light energy from an optical fiber in which inconjunction with a cooling fluid which is supplied through a conduitwith the fiber to apply surface cooling and prevent surface damage whileallowing increased levels of energy to be applied to deeper tissues.This arrangement however provides no feedback control of the heatingeffect.

U.S. Pat. No. 5,785,704 (Bille) assigned to MRC Systems GmbH issued Jul.28, 1996 discloses a particular arrangement of laser beam and lens foruse in irradiation of brain tumors but does not disclose methods offeedback control of the energy. This arrangement uses high speed pulsedlaser energy for a photo-disruption effect.

Kahn, et al. in Journal of Computer Assisted Tomography 18 (4):519-532,July/August 1994; Kahn, et al. in Journal of Magnetic Resonance Imaging8: 160-164, 1998; and Vogl, et al. in Radiology 209: 381-385, 1998 alldisclose a method of application of heat energy from a laser through afiber to a tumor where the temperature at the periphery of the tumor ismonitored during the application of the energy by MRI. However none ofthese papers describes an arrangement in which the energy is controlledby feedback from the monitoring arrangement. The paper of Vogl alsodiscloses a cooling system supplied commercially by Somatex of BerlinGermany for cooling the tissues at the probe end. The system is formedby an inner tube through which the fiber passes mounted within an outertube arrangement in which cooling fluid is passed between the two tubesand inside the inner tube in a continuous stream.

BRIEF SUMMARY OF THE INVENTION

It is one object of the present invention, therefore, to provide animproved method and apparatus for effecting treatment of a patient byhyperthermia.

According to a first aspect of the invention there is provided a methodfor effecting treatment in a patient comprising:

-   Identifying a volume in the patient the whole of which volume is to    be heated to a required temperature, the volume being defined by a    peripheral surface of the volume;-   providing a heat source and applying heat to the volume within the    patient by;-   providing the heat source on an invasive probe having a longitudinal    axis and an end;-   inserting the end of the probe into the volume;-   arranging the probe to cause directing of heat from the end in a    direction at an angle to the longitudinal axis such that a heating    effect of the probe lies in a disk surrounding the axis;-   arranging the direction of the heat so as to define a heating zone    which forms a limited angular orientation of heating within the disk    such that, as the probe is rotated, the probe causes heating of    different angular segments of the volume within the disk;-   with the probe at a fixed axial position, rotating the probe about    the axis so that the heating zone lies in a selected segment;-   wherein the application of heat by the probe to the selected segment    causes heat to be transferred from the segment into parts of the    volume outside the segment surrounding the end of the probe;-   and applying cooling to the end of the probe so as to extract heat    from the parts surrounding the probe by conduction of heat    therefrom.

Cooling of the probe may be optional. For example, when utilizingfocused ultrasound and e-beam energy, cooling may not be as relevant ormay not be required. With ultrasound energy, fluid may be used as theconduction medium as more specifically describe below. When cooling isused, preferably the amount of cooling to the probe is arranged relativeto the heating such that the parts of the volume surrounding the end ofthe probe are cooled sufficiently to cause a net heating effect by whichsubstantially only the segment of the heating zone is heated to therequired temperature and the parts outside the segment are not heated tothe required temperature. This is preferably arranged so that thecooling maintains the parts outside the segment below a temperaturesufficient to cause coagulation of the tissues therein. Thus when theprobe is rotated to take up a new angle within a new segment, the tissuein the new segment is not in a condition by pre-heating that wouldinterfere with the transmission and diffusion of the heat to thatsegment.

The arrangement of the present invention, that is the method definedabove or the method or probe defined hereinafter, can be used on a rigidprobe which is intended to be inserted in a straight line into aspecific location in the body of the patient, or can be used on aflexible probe which can be guided in movement through a part of thebody such as a vein or artery to a required location.

While the most likely and currently most suitable energy source is thatof laser light, the arrangements described and defined herein can alsobe used with other energy sources of the type which can be directed atan angle from the axis of the probe through which they are supplied suchas electron beams or ultrasound generators.

In one exemplary arrangement, the above method can be used with MRI realtime control of the surgery by which a non-invasive detection system,such as MR1, is operated to generate a series of output signals over aperiod of time representative of temperature in the patient as thetemperature of the patient changes during that time. The output signalsare used to monitor at least one temperature of the volume as thetemperature changes over the period of time. The application of heat tothe probe is then controlled in response to the changes in temperaturewherein the temperature at the peripheral surface of the volume ismonitored and a measure of the temperature at a location on theperipheral surface of the volume is used as the determining factor as towhen to halt heating by the probe to the location. However the coolingeffect can be used without the MRI monitoring to provide an enhancedsystem in which the whole of the volume required can be heated to therequired temperature.

In the method in which temperature is monitored, the determination as towhen to halt heating by the probe to the location is made based upon thetemperature at the peripheral surface of the volume, with the exceptionthat temperatures within the volume may be monitored to ensure that noserious or dangerous over-temperature occurs within the volume due tounexpected or unusual conditions. Thus any such over-temperature may bedetected and used to halt further treatment or to trigger an alarm tothe doctor for analysis of the conditions to be undertaken.

When used as a rigid probe for treatment within a body part such as thebrain or liver, the probe itself may be sufficiently rigid and strong toaccommodate the forces involved and not require the use of a cannula or,alternatively, there may be provided a cannula through which the probeis inserted, the cannula having an end which is moved to a positionimmediately adjacent but outside the volume and the probe having a rigidend portion projecting from the end of the cannula into the volume. Whenused as a non-rigid probe for treatment within a body part such as thebrain or liver, the probe itself may require the use of a cannulathrough which the probe is inserted as described herein.

In one embodiment of the present invention, the heat source comprises alaser, an optical fiber for communicating light from the laser and alight-directing element at an end of the fiber for directing the lightfrom the laser to the predetermined direction relative to the fiberforming the limited angular orientation within the disk.

In accordance with one embodiment of the present invention whichprovides the necessary level of cooling in a readily controllableprocess, the end of the probe is cooled by liquid-to-liquid,liquid-to-gas and gas-to-gas cooling by:

-   providing on the probe a supply duct for a cooling fluid extending    from a supply to the end of the probe;-   providing an expansion zone of reduced pressure at the end of the    probe so as to cause the cooling fluid to expand as a gas thus    generating a cooling effect;-   and providing on the probe a return duct for return of the expanded    gas from the end of the probe.

In this arrangement, the return duct is preferably of largercross-sectional area than the supply duct and the supply duct includes arestricting orifice at its end where the return duct is larger incross-sectional area by a factor of the order of 200 times larger thanthe orifice of the supply duct.

Preferably where the probe comprises a tube the supply duct is arrangedinside the tube and the return duct is defined by an inside surface ofthe tube.

In this arrangement, the supply duct is attached as tube to an insidesurface of the tube and the fiber itself is attached also to the inside.

In this arrangement, the orifice is provided by a restricting valve orneck in the supply duct immediately upstream of the expansion chamber atthe end of the probe.

Where the fiber has a chamfered end of the fiber it may include areflecting coating thereon for directing the light energy to the side.The arrangement of the chamfered end can have the advantage or featurethat the chamfered end is located in the gas rather than being wetted bycooling fluid which can, when there is no coating, interfere with thereflective properties of the coating and thus with the proper controland direction of the light.

In this arrangement, the chamfered end can be arranged directly at 45degrees to provide a light direction lying wholly in a radial plane atright angles to the axis of the fiber. The chamfered end may carry acoating arranged to reflect light at two different wavelengths.

In order to accurately control the cooling effect to maintain the netheating required, there is preferably provided a temperature sensor atthe end of the probe, which may be located inside the tube with theconnection therefor passing through the probe to the control systemoutside the probe.

Preferably the temperature at the end of the probe is controlled byvarying the pressure in the fluid as supplied through the supply duct.This system can allow the temperature to be maintained between aboutzero and minus 20 degrees Celsius, which provides the required level ofcooling to the probe for the net heating effect.

According to a second aspect of the invention there is provided a methodfor effecting treatment in a patient comprising:

-   identifying a volume in the patient to be heated to a required    temperature;-   providing a heat source for applying heat to the volume within the    patient,-   providing a probe mounting the heat source allowing invasive    insertion of an end of the probe into the patient,-   providing a position control system for moving the end of the probe    to a required position within the patient;-   inserting the end of the probe into the volume;-   providing on the probe a supply duct for a cooling fluid extending    from a supply to the end of the probe;-   providing an expansion zone of reduced pressure at the end of the    probe so as to cause the cooling fluid to expand as a gas thus    generating a cooling effect;-   and providing on the probe a return duct for return of the expanded    gas from the end of the probe.

According to a third aspect of the invention there is provided a probefor use in effecting treatment in a patient comprising:

-   a heat source for applying heat to a volume within the patient,-   a probe body mounting the heat source thereon for allowing invasive    insertion of an end of the probe into the patient,-   a supply duct on the probe body for a cooling fluid extending from a    supply to the end of the probe;-   the probe body being arranged to provide an expansion zone of    reduced pressure at the end of the probe body so as to cause the    cooling fluid to expand as a gas thus generating a cooling effect;-   and a return duct on the probe body for return of the expanded gas    from the end of the probe.

According to a fourth embodiment of the present invention there isprovided a method of applying heat to tissue in vivo comprising:

-   identifying a quantity of tissue as a target;-   inserting an elongate transmitting medium percutaneously and feeding    said elongate transmitting medium toward said target until a distal    end of said elongate transmitting medium is operationally proximate    said target;-   applying energy to said target by sending energy through said    elongate transmitting medium, said energy exiting said distal end    and heating said target;-   monitoring said energy application to ensure surrounding    non-targeted tissue is not damaged by heat;-   determining whether the entire targeted area has been heated;-   if necessary, translating said elongate transmitting medium to an    unheated area of said target;-   applying energy to said unheated area of said target.

The step of identifying a quantity of tissue as a target may beaccomplished by analyzing magnetic resonance images and mapping out theextents of a tumor imaged thereby; or by conducting a body contouringanalysis to determine areas of fatty tissue to be removed; or byanalyzing magnetic resonance images to locate a lesion imaged thereby.

The step of inserting an elongate transmitting medium percutaneously andfeeding said elongate transmitting medium toward said target until adistal end of said elongate transmitting medium is operationallyproximate said target may be accomplished by:

-   determining a safest straight path between the skull and the target;-   forming a hole in the skull;-   inserting said elongate transmitting medium through said hole toward    said target until said distal end of said elongate transmitting    medium is operationally proximate said target

Alternatively, the step of inserting an elongate transmitting mediumpercutaneously may include the step of inserting a cannula into saidhole until a distal end of said cannula is operably proximate saidtarget;

-   securing the cannula relative the skull;-   and inserting said elongate transmitting medium through said cannula    toward said target until said distal end of said elongate    transmitting medium is operationally proximate said target;-   or by:-   inserting said elongate transmitting medium in an artery;-   feeding said elongate transmitting medium through the artery until a    distal end of the elongate transmitting medium is operationally    proximate a lesion or other target;-   or by percutaneously inserting the elongate transmitting medium    proximate an area of fat targeted for heat treatment.

The step of applying energy to the target through the elongatetransmitting medium may be accomplished by sending light, laser,collimated, or non-collimated, through an optical fiber. Morespecifically, this step may be accomplished by:

-   a) causing said energy to exit said distal end at an angle, greater    than zero, to a longitudinal axis of the elongate transmitting    medium;-   b) rotating said elongate transmitting medium around said    longitudinal axis, thereby creating a shaped area of treated tissue;-   c) advancing said elongate transmitting medium;-   d) repeating steps a)-c) until the entire target has been heated.

Step a) may be accomplished by causing said energy to exit said distalend approximately perpendicularly to said longitudinal axis of theelongate transmitting medium such that performing step b) results in ashaped area of treated tissue that is disc-shaped; or by causing saidenergy to exit said distal end at an angle other than perpendicular tosaid longitudinal axis of the elongate transmitting medium such thatperforming step b) results in a shaped area of treated tissue that iscone-shaped.

Alternatively, the step of applying energy to said target by sendingenergy through said elongate transmitting medium, said energy exitingsaid distal end and heating said target, may be accomplished by allowingsaid energy to exit said distal end along a longitudinal axis of theelongate transmitting medium.

The step of monitoring said energy application to ensure surroundingnon-targeted tissue is not damaged by heat may be accomplished by takingtemperature readings on non-targeted tissue immediately adjacent saidtargeted tissue; or by cycling cooling fluid to and from the distal endof the elongate transmitting medium as necessary to prevent damagingsaid surrounding nontargeted tissue.

A fifth embodiment of the present invention provides a method ofdestroying unwanted fat cells comprising:

-   a) identifying fat cells to be destroyed thereby defining a target    that is a volume of fat cells;-   b) percutaneously inserting a probe having a distal end capable    emitting energy;-   c) positioning said probe such that said distal end is operationally    proximate said target;-   d) emitting energy from the distal end of the probe sufficient to    destroy fat cells;-   e) moving the distal end of the probe through the volume of fat    cells and emitting energy from the distal end, either successively    or simultaneously, until the targeted volume of fat cells has been    destroyed.

This method may also include cooling the distal end of the probe toprevent overheating cells that are not included in the volume of fatcells.

A sixth embodiment of the present invention provides a method ofcoagulating blood in a vascular lesion that includes

-   a) identifying a vascular lesion;-   b) percutaneously inserting a probe having a distal end capable    emitting energy;-   c) positioning said probe such that said distal end is operationally    proximate said lesion;-   d) emitting energy from the distal end of the probe sufficient to    coagulate said vascular lesion-   wherein said coagulation results in cessation or reduction of flow    to said vascular lesion.

Step b) may include forming an entry hole in the skull of the patient,fastening a cannula to the entry hole that is constructed and arrangedto create an insertion path for a rigid or nonrigid probe that is aimeddirectly at the lesion, and inserting the probe into the cannula.

A seventh embodiment of the present invention provides a method ofrepairing, reconstruction or removing tissue comprising:

-   a) identifying a target that comprises healthy tissue to be    repaired, reconstructed or removed;-   b) percutaneously inserting a probe having a distal end capable    emitting energy;-   c) positioning said probe such that said distal end is operationally    proximate said target;-   d) emitting energy from the distal end of the probe sufficient to    repair, reconstruct or remove said target;-   e) moving the distal end of the probe through the target tissue and    emitting energy from the distal end, either successively or    simultaneously, until the targeted volume has been repaired,    reconstructed or removed.

This method may also include cooling the distal end of the probe toprevent overheating cells that are not included in the targeted tissue.

The method may also include targeting healthy tissue or targeting scartissue.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an apparatus for effecting MRIguided laser treatment according to the present invention.

FIG. 2 is a schematic illustration of the apparatus of FIG. 1 on anenlarged scale and showing the emission of laser energy into the brainof a patient.

FIG. 3 is a side elevation of the laser probe of the apparatus of FIG.1.

FIG. 4 is an end elevation of the laser probe of the apparatus of FIG.1.

FIG. 5 is a cross-sectional view of the laser probe and drive motortherefor of the apparatus of FIG. 1.

FIG. 6 is an exploded view of the drive motor of the apparatus of FIG.1.

FIG. 7 is a schematic illustration of the shielding of the apparatus ofFIG. 1.

FIG. 8 is a schematic illustration of the effect of the apparatus on atumor or other lesion to be coagulated.

FIG. 9 is a longitudinal cross-sectional view through an alternativeform of a probe that provides a flow of cooling fluid to the end of theprobe for cooling the surrounding tissue.

FIG. 10 is a cross-sectional view along the lines 10-10 of FIG. 9.

FIG. 11 is a longitudinal cross-sectional view through a furtheralternative form of probe which provides a flow of cooling fluid to theend of the probe for cooling the surrounding tissue.

FIG. 12 is a cross-sectional view along the lines 12-12 of FIG. 11.

FIG. 13 is a photograph of a cross-section of a tissue sample that hasbeen heated in three separate segments showing the absence of heatingoutside the segments.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 is shown schematically an apparatus for carrying out MRIcontrolled laser treatment. The apparatus comprises a magnetic resonanceimaging system including a magnet 10 provided within a shielded room 11.The magnet 10 can be of any suitable construction and many differentmagnet arrangements are available from different manufacturers. Themagnet includes field coils for generating variations in the magneticfield which are not shown since these are well known to one skilled inthe art together with a radio frequency antenna coil which receivessignals from the sample in this case indicated as a human patient 13.

The patient 13 rests upon a patient support table 14 on which thepatient is supported and constrained against movement for the operativeprocedure. The fields of the magnet are controlled on an input controlline 15 and the output from the antenna coil is provided on an outputline 16 both of which communicate through a surgeon interface 17 to theconventional MRI control console 18. The MRI console and the magnet areshown only schematically since these are well known to one skilled inthe art and available from a number of different manufacturers.

The apparatus further includes a laser treatment system including anoptical fiber assembly 20 that transmits heat energy in the form oflight from a laser 21 mounted outside the room 11. The fiber assembly 20extends from the laser 21 to a terminus 36 (FIG. 2), from which theenergy escapes into the relevant part of the patient 13 as discussedhereinafter. The position of the fiber assembly 20 within the patient 13and the orientation of the fiber are controlled by a drive motor 22supported in fixed adjustable position on a stereotaxic frame 23. Themotor communicates through a control line 24 to a device controller 25.In general the device controller 25 receives information from the MRIconsole 18 and from position detectors of the motor 22 and uses thisinformation to control the motor 22 and to operate a power output fromthe laser 21, thereby controlling the position and amount of heat energyapplied to the part within the body of the patient 13.

In FIG. 2 is shown on a larger scale the patient table 14. Thestereotaxic frame 23 is attached to the table 14 and extends over thehead 26 of the patient 13. The frame 23 is shown schematically andsuitable details will be well known to one skilled in the art, butcarries the motor 22 in a position on the frame 23 through the use of amotor bracket 27. The position of the motor 22 on the frame 23 remainsfixed during the procedure but can be adjusted in the arcuate direction28 around the arch of the frame 23. The frame 23 can also be adjustedforwardly and rearwardly on the table 14. The bracket 27 also allowsrotation of the motor 22 about a point 30 within the frame 23 so thatthe direction of the fiber assembly 20 projecting forwardly from themotor 22 can be changed relative to the frame. 23.

Referring now to FIG. 3, the basic components of the fiber assembly 20of the apparatus are shown. The fiber assembly 20 includes a rigidcannula 31 surrounding a glass fiber element 35, and arranged to allowsliding and rotational movement of the fiber element 35 within thecannula 31 while holding the fiber element 35 in a direction axial ofthe cannula. 31. The cannula 31 is formed of a suitable rigid MRIcompatible material such as ceramic so that it is stiff and resistant tobending and has sufficient strength to allow the surgeon to insert thecannula 31 into the required location within the body part of thepatient. 13.

In the arrangement as shown, the apparatus is arranged for operatingupon a tumor 32 (FIG. 2) within the brain 33 of the patient. 13. Thesurgeon therefore creates an opening 34 in the skull of the patient 13and directs the cannula 31, in the absence of the rest of the fiberassembly 20, through the opening 34 to the front edge of the tumor 32.The cannula 31, once in place, will act as a guide for the remainder ofthe fiber assembly 20.

The position of the tumor 32 is determined in an initial set of MRIexperiments using conventional surgical and an analytical techniques todefine the boundaries, that is a closed surface within the volume of thebrain 33 which constitutes the extremities of the tumor 32. The surgicalanalysis by which the surgeon determines exactly which portions of thematerial of the patient 13 should be removed is not a part of thisinvention except to say that conventional surgical techniques areavailable to one skilled in the art to enable an analysis to be carriedout to define the closed surface.

The angle of insertion of the cannula 31 is selected to best avoidpossible areas of the patient 13 that should not be penetrated, such asmajor blood vessels, and also so the cannula 31 is pointed toward acenter of the tumor 32.

The fiber assembly 20 further includes an actual glass fiber element 35,which has an inlet end (not shown) at the laser 21 and a terminus 36. Atthe terminus 36 is provided a reflector or prism, which directs thelaser energy in a beam 37 to one side of the terminus 36. Thus the beam37 is directed substantially at right angles to the length of the fiberand over a small angle around the axis of the fiber. The beam 37 forms acone having a cone angle of the order of 12 to 15 degrees. Such fibersare commercially available including the reflector or prism fordirecting the light at right angles to the length of the fiber.

The fiber element 35 is encased to allow the fiber element 35 to bemanipulated in the motor 22. Around the fiber element 35 is a sleeve 38including a first end portion 39 and a longer second portion 40. The endportion 39 encloses the terminus 36, which is spaced from a tip 41 ofthe end portion 39. The end portion 39 has a length on the order of 7 to11 cm. The second portion 40 is on the order of 48 to 77 cm in lengthand extends from a forward end 141 through to a rear end 42. The firstend portion 39 is formed of a rigid material such as glass. The secondportion 40 is formed of a stiff material which is less brittle thanglass and yet maintains bending and torsional stiffness of the fiberelement 35 so that forces can be applied to the second portion 40 tomove the terminus 36 of the fiber element 35 to a required positionwithin the tumor 32. The second portion 40 is formed of a material suchas fiber-reinforced plastics.

The two portions 39 and 40 are bonded together to form an integralstructure of common or constant diameter selected as a sliding fitthrough the cannula 31. The first end portion 39 and the cannula 31 aresized so that it the first end portion 39 can extend from the distal endof the cannula 31 and reach a distal end of the tumor 32. An averagetumor might have a diameter of the order of 0.5 to 5.0 cm so that theabove length of the forward portion is sufficient to extend through thefull diameter of the tumor 32 while leaving a portion of the order of1.25 cm within the end of the cannula 31. In this way, the substantiallyrigid first end portion 39 remains relatively coaxial with the cannula31.

The second portion 40 has attached to it a polygonal or non-circularsection 44 and a stop section 45, both of which act as attachment pointsfor rotational and longitudinal sections, respectively. Thus thepolygonal section 44 is arranged to co-operate with a drive member thatacts to rotate the second portion 40 and therefore the fiber element 35.The stop section 45 is arranged to co-operate with a longitudinallymovable drive element that moves the second portion 40, and thereforethe fiber element 35, longitudinally. In this way the terminus 36 can bemoved from an initial position, just beyond the outer end of the cannula31, outwardly into the body of the tumor 32 until the tip reaches thefar end of the tumor 32. In addition the terminus 36 can be rotatedaround the axis of the fiber element 35 so that heat energy can beapplied at selected angles around the axis. By selectively controllingthe longitudinal movement and rotation of the terminus 36, therefore,heat energy can be applied throughout a cylindrical volume extendingfrom the end of the cannula 31 along the axis of the cannula 31 awayfrom the end of the cannula. 31. In addition by controlling the amountof heat energy applied at any longitudinal position and angularorientation, the heat energy can be caused to extend to required depthsaway from the axis of the cannula 31 so as to effect heating of the bodypart of the patient 13 over a selected volume with the intention ofmatching the volume of the tumor 32 out to the predetermined closedsurface area defining the boundary of the tumor 32.

As shown in FIG. 4, the non-circular cross-section of section 44 isrectangular with a height greater than the width. However of courseother non-circular shapes can be used provided that the cross-section isconstant along the length of the non-circular section 44 and providedthat the non-circular section 44 can co-operate with a surrounding drivemember to receive rotational driving force therefrom. The stop section45 is generally cylindrical with a top segment 45A removed to assist theoperator in insertion of the fiber into the drive motor.

Turning now to FIGS. 5 and 6, the drive motor 22 is shown in more detailfor effecting a driving action on the fiber through the sections 44 and45 into the sleeve 38 for driving longitudinal and rotational movementof the terminus 36.

The drive motor comprises a housing 50 formed by an upper half 51 and alower half 52 both of semi-cylindrical shape with the two halves engagedtogether to surround the sections 44 and 45 with the sleeve 38 extendingaxially along a center of the housing. 50. At the front 53 of thehousing 50 is provided a boss defining a bore 54 within which the sleeve38 forms a sliding fit. This acts to guide the movement of the sleeve atthe forward end of the housing.

Within the housing is provided a first annular mount 55 and a secondannular mount 56 spaced rearwardly from the first. Between the firstannular mount 55 and the front boss is provided a first encoder 57 andbehind the second annular mount 56 is provided a second encoder 58. Thefirst annular mount 55 mounts a first rotatable drive disk 59 onbearings 60. The second annular mount carries a second drive disk 61 onbearings 62. Each of the drive disks is of the same shape including agenerally flat disk portion with a cylindrical portion 63 on the rear ofthe disk and lying on a common axis with the disk portion. The bearingsare mounted between a cylindrical inner face of the annular portion 55,56 and an outside surface of the cylindrical portions 63. Each of thedisks is therefore mounted for rotation about the axis of the fiberalong the axis of the housing.

The disk 59 includes a central plug portion 64, which closes the centerhole of the disk portion and projects into the cylindrical portion 63.The plug portion has a chamfered or frustoconical lead in section 65converging to a drive surface 66 surrounding the section 44 and having acommon cross-sectional shape therewith. Thus the tip portion 41 of thesleeve 38 can slide along the axis of the housing and engage into theconical lead in section 65 so as to pass through the drive surface orbore 66 until the section 44 engages into the surface 66. In theposition, rotation of the disk 59 drives rotation of the sleeve 38 andtherefore of the fiber. As the noncircular section 44 has a constantcross-section, it can slide through the drive surface 66 forwardly andrearwardly.

The disk 61 includes a plug member 67, which engages into the centralopening in the disk member 61. The plug 67 has an inner surface 68,which defines a female screw thread for co-operating with a lead screw69. The lead screw 69 has an inner bore 70 surrounding the sleeve 38 sothat the sleeve 38 is free to rotate and move relative to the bore 70.The lead screw 69 also passes through the cylindrical portion 63 of thedisk 61. Rotation of the disk 61 acts to drive the lead screwlongitudinally along the axes of the housing and the sleeve 38. A rearend 71 of the lead screw is attached to a clamping member 72. Theclamping member 72 includes a first fixed portion 73 attached to therear end 71 of the lead screw and a second loose portion 74 which can beclamped into engaging the fixed portion so as to clamp the end stopmembers 45 in position within the clamping member. The loose portion 74is clamped in place by screws 75. The top segment 45A of the end stop 45engages into a receptacle 76 in the fixed portion 73 so as to orient thesleeve 38 relative to the lead screw.

The disks 59 and 61 are driven in a ratcheting action by drive motors 77and 78 respectively. In an exemplary embodiment the drive motors areprovided by piezoelectric drive elements in which a piezoelectriccrystal is caused to oscillate thus actuating a reciprocating actionthat is used to drive by a ratchet process angular rotation of therespective disk.

The reciprocating action of the piezoelectric crystal 77 and 78 isprovided by two such motors 77 co-operating with the disk 59 and twomotors 78 co-operating with the disk 61. Each motor is carried on amounting bracket 77 A, 78A that is suitably attached to the housing. Theend clamp 72 is generally rectangular in cross-section and slides withina correspondingly rectangular cross-section duct 72A within the housing.Thus the lead screw 69 is held against rotation and is driven axially bythe rotation of the disk 61 while the fiber is free to rotate relativeto the lead screw. The use of a piezoelectric crystal to drive disks isparticularly suitable and provides particular compatibility with the MRIsystem but other drive systems can also be used as set forth previously.

In other alternative arrangements (not shown), the ratcheting action canbe effected by a longitudinally moveable cable driven from the devicecontroller 25 outside the room 11. In a further alternative arrangement,the motor may comprise a hydraulic or pneumatic motor which againeffects a ratcheting action by reciprocating movement of a pneumaticallyor hydraulically driven prime mover. Thus selected rotation of arespective one of the disks can be effected by supplying suitable motivepower to the respective motor.

The respective encoder 57, 58 detects the instantaneous position of thedisk and particularly the sleeve portion 63 of the disk, which projectsinto the interior of the encoder. The sleeve portion therefore carries asuitable element, which allows the encoder to accurately detect theangular orientation of the respective disk. In this way the position ofthe disks can be controlled by the device controller 25 accuratelymoving the disk 59 to control the angular orientation of the fiber andaccurately moving the disk 61 to control the longitudinal position ofthe fiber. The longitudinal position is obtained by moving the leadscrew, which carries the end stop 45. The movements are independent sothat the fiber can be rotated while held longitudinally stationary.

As the motor driving movement of the fiber is used while the magnet andthe MRI system is in operation, it is essential that the motor and theassociated control elements that are located within the room 11 arecompatible with the MRI system. For this purpose, the power supply orcontrol cable 24 and the motor must both be free from ferromagneticcomponents that would be responsive to the magnetic field. In additionit is necessary that the motor 22 and the cable 24 are both properlyshielded against interference with the small radio frequency signalsthat must be detected for the MRI analysis to be effective.

Referring now to FIG. 7, the room 11 is shielded to prevent radio wavesfrom penetrating the walls of the room 11 and interfering with theproper operation of the MRI machine 10. Additionally, the cable 24 andthe motor 22 are surrounded by a conductor 80, which extends through anopening 81 in the wall of the room 11. The conductor also passes througha cable port 82 within a wall 83 of the enclosure so that the whole ofthe motor and the cable are encased within the conductor 80.

In the method of operation, the patient 13 is located on the patienttable and restrained so that the head of the patient 13 remainsmotionless to prevent motion artifacts. The MRI system is then operatedin conventional manner to generate images of the targeted tumor 32. Theimages are used to determine the size and shape of the tumor 32 and todefine the external perimeter 90 of the tumor 32 (FIG. 8). The surgeonalso determines an optimal location to place the cannula 31 so that thecannula 31 is aimed at the targeted tumor 32 without causing damage tosurrounding tissue. Next, the opening 34 is formed in the skull of thepatient 13 and the cannula 31 inserted.

With the cannula 31 in place, the motor 22 is mounted on the frame 23and the frame 23 adjusted to locate the motor 22 so that the fiberassembly 20 can be inserted directly into the cannula. 31. With themotor 22 properly aligned along the axis of the cannula, 31, the fiberassembly 20 is inserted through the bore of the motor 22 and into thecannula 31 so as to extend through the cannula 31 until the terminus 36emerges just out of the outer end of the cannula 31. The distance of themotor from the cannula 31 can be adjusted so that the terminus 36 justreaches the end of the cannula 31 when the lead screw is fully retractedand the end stop is located in place in the clamp 72.

With the motor and fiber thus assembled, the MRI system measurestemperatures in the boundary zone 90. The temperature is detected overthe full surface area of the boundary rather than simply at a number ofdiscrete locations. While the measurements are taken, the fiber is movedlongitudinally to commence operation at a first position just inside thevolume of the tumor 32. At a selected angular orientation of the beam,pulses of radiation are emitted by the laser and transmitted into thetumor 32 through the beam 37. The pulses are continued while thetemperature in the boundary layer 90 is detected. As the pulses supplyheat energy into the volume of the tumor 32, the tumor 32 is heatedlocally basically in the segment shaped zone defined by the beam butalso heat is conducted out of the volume of the beam into the remainderof the tumor 32 at a rate dependant upon the characteristics of thetumor 32 itself. Heating at a localized area defined by the beam istherefore continued until the heat at the boundary layer 90 is raised tothe predetermined coagulation temperature on the order of 55 to 65 C.Once the boundary layer reaches this temperature, heating at thatsegment shaped zone within the disk is discontinued and the fiber ismoved either longitudinally to another disk or angularly to anothersegment or both to move to the next segment shaped zone of the tumor 32to be heated. It is not necessary to predict the required number ofpulses in advance since the detection of temperature at the boundary isdone in real time and sufficiently quickly to prevent overshoot.However, predictions can be made in some circumstances in order to carryout the application of the heat energy as quickly as possible byapplying high power initially and reducing the power after a period oftime.

It is desirable to effect heating as quickly as possible so as tominimize the operation duration. Heating rate may be varied by adjustingthe number of pulses per second or the power of the heat source. Care istaken to vary these parameters to match the characteristics of the tumor32, as detected in the initial analysis. Thus the system may vary theenergy pulse rate or power-time history of the heat source to modify thepenetration depth of the heat induced lesion so that it can control theheating zone of an irregularly shaped lesion. The energy applicationrate should not be high enough to result in over heating the tissueoutside of the perimeter of the tumor. The rate of heat application canalso be varied in dependence upon the distance of the boundary from theaxis of the fiber. Thus, the axis of the fiber is indicated at 91 inFIG. 8 and a first distance 92 of the beam to the boundary is relativelyshort at the entry point of the fiber into the tumor 32 and increases toa second larger distance 93 toward the center of the tumor 32. Inaddition to pulses per second, it is also possible to adjust thepower-time history of the laser energy to maximize penetration into thelesion. That is to use high power first for a short period of time andthen ramp the power down throughout the duration of the treatment atthat particular location.

In some cases it is desirable to maintain the fiber stationary at afirst selected longitudinal position and at a first selected angularorientation until the temperature at the boundary reaches the requiredtemperature. In this case the fiber is then rotated through an angleapproximately equal to the beam angle to commence heating at a secondangular orientation with the fiber being rotated to a next angularorientation only when heating at that second orientation is complete. Inthis way heating is effected at each position and then the fiber rotatedto a next orientation position until all angular orientations arecompleted.

After a first disk shaped portion of the tumor 32 is thus heated, thefiber is moved longitudinally through a distance dependant upon thediameter of the tumor 32 at that location and dependant upon the beamangle so as to ensure the next heated area does not leave unheated tumortissue between the two successive disk shaped areas. Thus the fiber ismoved longitudinally in steps, which may vary in distance depending uponthe diameter and structure of the tumor 32 as determined by the initialanalysis. However the total heating of the tumor 32 is preferablydetermined by the temperature at the boundary without the necessity foranalysis of the temperatures of the tumor 32 inside the boundary or anycalculations of temperature gradients within the tumor 32. When thecomplete boundary of the tumor 32 has been heated to the predeterminedcoagulation temperature, the treatment is complete and the apparatus ISdisassembled for removal of the fiber assembly 20 and the cannula 31from the patient 13.

The system allows direct and accurate control of the heating bycontrolling the temperature at the surface area defined by the boundaryof the tumor 32 so that the whole of the volume of the tumor 32 isproperly heated to the required temperature without heating areasexternal to the tumor 32 beyond the coagulation temperature. In order tomaximize the amount of heat energy which can be applied through thefiber and thereby to effect treatment of larger tumors, it is highlydesirable to effect cooling of the tissue immediately surrounding theend of the fiber so as to avoid overheating that tissue. Overheatingbeyond the coagulation temperature is unacceptable, as it will causecarbonization, which will inhibit further transmission of the heatenergy. Without cooling it is generally necessary to limit the amount ofheat energy that is applied. As energy dissipates within the tissue,such a limitation in the rate of application of energy limits the sizeof the tumor to be treated since dissipation of energy prevents theoutside portions of the tumor from being heated to the requiredcoagulation temperature.

In FIGS. 9 and 10 is therefore shown a modified laser probe which can beused in replacement for the probe previously described, bearing in mindthat it is of increased diameter and thus minor modifications to thedimensions of the structure are necessary to accommodate the modifiedprobe.

The modified probe 100 comprises a fiber 101 which extends from a tipportion 102 including the light dispersion arrangement previouslydescribed to a suitable light source at an opposed end of the fiber aspreviously described. The probe further comprises a support tube 103 inthe form of a multi-lumen extruded plastics catheter for the fiber whichextends along the fiber from an end 104 of the tube just short of thetip 102 through to a position beyond the fiber drive system previouslydescribed. The tube 103 thus includes a cylindrical duct 104 extendingthrough the tube and there are also provided two further ducts 105 and106 parallel to the first duct and arranged within a cylindrical outersurface 107 of the tube.

The supporting tube 103 has at its end opposite the outer end 104 acoupling 108 which is molded onto the end 109 and connects individualsupply tubes 110, 111 and 112 each connected to a respective one of theducts 104, 105 and 106. Multi-lumen catheters of this type arecommercially available and can be extruded from suitable material toprovide the required dimensions and physical characteristics. Thus theduct 104 is dimensioned to closely receive the outside diameter of thefiber so that the fiber can be fed through the duct tube 110 into theduct 104 and can slide through the support tube until the tip 102 isexposed at the end 104.

While tubing may be available which provides the required dimensions andrigidity, in many cases, the tubing is however flexible so that it bendsside to side and also will torsionally twist. The support tube istherefore mounted within an optional stiffening tube or sleeve 114,which extends from an end 115 remote from the tip 102 to a second end106 adjacent to the tip 102. The end 116 is however spaced rearwardlyfrom the end 104 of the tubing 103, which in turn is spaced from the tip102. The distance from the end 106 to the tip 102 is arranged to be lessthan a length of the order of 1 inch. The stiffening tube 114 is formedof a suitable stiff material that is non-ferro-magnetic so that it isMRI compatible. The support tube 103 is bonded within the stiffeningtube 114 so that it cannot rotate within the stiffening tube and cannotmove side to side within the stiffening tube. The stiffening tube ispreferably manufactured from titanium, ceramic or other material thatcan accommodate the magnetic fields of MRI. Titanium generates anartifact within the MRI image. For this reason the end 116 is spaced asfar as possible from the tip 102 so that the artifact is removed fromthe tip to allow proper imagining of the tissues.

At the end 116 of the stiffening tube 114 is provided a capsule 120 inthe form of a sleeve 121 and domed or pointed end 122. The sleevesurrounds the end 116 of the stiffening tube and is bonded thereto so asto provide a sealed enclosure around the exposed part of the tube 103.The capsule 120 is formed of quartz crystal so as to be transparent toallow the escape of the disbursed light energy from the tip 102. Thedistance of the end of the stiffening tube from the tip is arranged suchthat the required length of the capsule does not exceed what can bereasonably manufactured in the transparent material required.

The tube 111 is connected to a supply 125 of a cooling fluid and thetube 112 is connected to a return collection 126 for the cooling fluid.Thus, the cooling fluid is pumped through the duct 105 and escapes fromthe end 104 of the tube 103 into the capsule and then is returnedthrough the duct 106. The cooling fluid can simply be liquid nitrogenallowed to expand to nitrogen gas at cryogenic temperatures and thenpumped through the duct 105 and returned through the duct 106 where itcan be simply released to atmosphere at the return 126.

In an alternative arrangement the supply 125 and the return 126 formparts of a refrigeration cycle where a suitable coolant is compressedand condensed at the supply end and is evaporated at the cooling zone atthe capsule 120 so as to transfer heat from the tissue surrounding thecapsule 120 to the cooling section at the supply end.

The arrangement set forth above allows the effective supply of thecooling fluid in gaseous or liquid form through the ducts 105 and 106and also effectively supports the fiber 101 so that it is held againstside to side or rotational movement relative to the stiffening tube 114.The location of the tip 102 of the fiber is therefore closely controlledrelative to the stiffening tube and the stiffening tube is driven bycouplings 130 and 131 shown schematically in FIG. 9 but of the typedescribed above driven by reciprocating motor arrangements as set forthhereinbefore.

In FIGS. 11 and 12 is shown the tip section of an alternative probe inwhich cooling of the tip section is effected using expansion of a gasinto an expansion zone. The tip only is shown as the remainder of theprobe and its movements are substantially as previously described.

Thus the probe comprises a rigid extruded tube 200 of a suitablematerial, for example titanium, that is compatible with MRI(non-ferromagnetic) and suitable for invasive medical treatment. Afurther smaller cooling fluid supply tube 202 is also separately formedby extrusion and is attached by adhesive to the inside surface of theouter tube. An optical fiber 204 is also attached by adhesive to theinside surface the outer tube so that the fiber is preferablydiametrically opposed to the tube 202.

The tube 202 is swaged at its end as indicated at 205, which projectsbeyond the end of the tube 201, to form a neck section of reduceddiameter at the immediate end of the tube 202. Thus in manufacture theextruded tube 201 is cut to length so as to define a tip end 207 atwhich the outer tube terminates in a radial plane. At the tip end beyondthe radial plane, the outer of the inner tube 202 is swaged by asuitable tool so as to form the neck section 205 having an internaldiameter of the order of 0.003 to 0.005 inch.

The fiber 204 is attached to the tube 201 so that a tip portion 208 ofthe fiber 204 projects beyond the end 207 to a chamfered end face 209 ofthe fiber which is cut at 45 degrees to define a reflective end plane ofthe fiber.

The end 207 is covered and encased by a molded quartz end cap 210 thatincludes a sleeve portion 211 closely surrounding the last part of thetube 200 and extending beyond the end 207 to an end face 212, whichcloses the capsule. The end face 212 is tapered to define a nose 213,which allows the insertion of the probe to a required location aspreviously described. The end of the tube 201 may be reduced in diameterso that the capsule has an outer diameter matching that of the mainportion of the tube. However in the arrangement shown the capsule isformed on the outer surface so that its outer diameter is larger thanthat of the tube and its inner diameter is equal to the outer diameterof the tube.

A thermocouple 214 is attached to the inside surface of the outer tube200 at the end 207 and includes connecting wires 215 which extend fromthe thermocouple to the control unit schematically indicated at 226.Thus the thermocouple provides a sensor to generate an indication of thetemperature at the end 207 within the quartz capsule. The quartz capsuleis welded to or bonded to the outer surface of the tube as indicated at215 so as to form a closed expansion chamber within the quartz capsulebeyond the end 207. The inner surface 216 of the quartz capsule is ofthe same diameter as the outer surface of the tube 200 so that theexpansion chamber beyond the end of the tube 200 has the same exteriordimension as the tube 200.

The quartz capsule is transparent so as to allow the reflected beam ofthe laser light from the end face 209 of the fiber to escape through thetransparent capsule in the limited angular direction substantially atright angles to the longitudinal axis of the fiber and within the axialplane defined by that longitudinal axis.

The tube 202 is connected at its end opposite to the tip to a fluidsupply 219, which forms a pressurized supply of a suitable cooling fluidsuch as carbon dioxide or nitrous oxide. The fluid supply 219 iscontrolled by the control unit 216 to generate a predetermined pressurewithin the fluid supply to the tube 202 which can be varied so as tovary the flow rate of the fluid through the neck 205. The fluid issupplied at normal or room temperature without cooling. The fluid isnormally a gas at this pressure and temperature but fluids that areliquid can also be used provided that they form a gas at the pressureswithin the expansion chamber and thus go through an adiabatic gasexpansion through the restricted orifice into the expansion chamber toprovide the cooling effect.

Thus the restricted orifice has a cross-sectional area very much lessthan that of the expansion chamber and the return duct provided by theinside of the tube 201. The items that reduce the effectivecross-sectional area of the return tube 201 are the optical fiber, thesupply tube, two thermocouple wires, the shrink tube that fixes thethermocouple wires to the optical fiber and the adhesives used to bondthe items into place (at the inlet of the discharge duct). Without thearea of the adhesives included in the calculation, the exhaust duct areais about 300 times larger than a delivery orifice diameter of 0.004″(the target size). When considering the area occupied by the adhesives,the exhaust duct inlet area would be approximately 200 to 250 timeslarger than the 0.004″ diameter orifice. Considering the manufacturingtolerance range of the supply tube orifice diameter alone, the exhaustduct area could be anywhere between 190 to 540 times larger than theorifice area (without considering the area occupied by adhesives). It isour estimation that a 200/1 gas expansion will be required to achieveappropriate cooling.

This allows the gas as it passes into the expansion chamber beyond theend 205 to expand as a gas thus cooling the quartz capsule and theinterior thereof at the expansion chamber to a temperature in the range−20 C to 0 C. This range has been found to be suitable to provide therequired level of cooling to the surface of the quartz capsule so as toextract heat from the surrounding tissue at a required rate. Variationsin the temperature in the above range can be achieved by varying thepressure from the supply 219 so that in one example the pressure wouldbe of the order of 700 to 850 psi at a flow rate of the order of 5liters per min.

The tube 202 has an outside diameter of the order of 0.014 inch OD,while the tube 203 has a diameter of the order of 0.079 inch. Thus adischarge duct for the gas from the expansion chamber is defined by theinside surface of the tube 200 having a flow area which is defined bythe area of the tube 200 minus the area taken up by the tube 202 and thefiber 207. This allows discharge of the gas from the expansion chamberdefined within the quartz capsule at a pressure of the order of 50 psiso that the gas can be simply discharged to atmosphere if inert or canbe discharged to an extraction system or can be collected for coolingand returned to the fluid supply 219 if economically desirable. Tipcooling is necessary for optimum tissue penetration of the laser orheating energy, reduction of tissue charring and definition of the shapeof the coagulated zone. The gas expansion used in the present inventionprovides an arrangement that is suitable for higher power densitiesrequired in this device to accommodate the energy supplied by the laserheating system.

The tip 208 of the fiber 204 is accurately located within the expansionzone since it is maintained in fixed position within the quartz capsuleby its attachment to the inside surface of the outer tube. The fiber islocated forwardly of the end 207 sufficiently that the MRI artifactgenerated by the end 207 is sufficiently removed from the plane of thefiber end to avoid difficulties in monitoring the temperature within theplane of the fiber end. The outlet orifice of the tube 202 is alsolocated forwardly of the end 207 so as to be located with the coolingeffect generated thereby at the plane of the fiber end.

The end face 209 is located within the expansion chamber 216 so that itis surrounded by the gas with no liquid within the expansion chamber.Thus, in practice there is no condensate on the end face 209 nor anyother liquid materials within the expansion chamber that would otherwiseinterfere with the reflective characteristics of the end face 209.

The end face 209 is coated with a reflective coating such as a dualdielectric film. This provides a reflection at the two requiredwavelengths of the laser light used as a visible guide beam and as theheat energy source such as He—Ne and Nd:YAG respectively. An alternativecoating is gold, which can alone provide the reflections at the twowavelengths.

The arrangement of the present invention provides excellent MRIcompatibility both for anatomic imaging as well as MR thermal profiling.Those skilled in the art will appreciate that the cooling system inaccordance with the present invention may also be used withcircumferential fibers having point-of-source energy.

In operation, the temperature within the expansion zone is monitored bythe sensor 214 so as to maintain that temperature at a predeterminedtemperature level in relation to the amount of heat energy suppliedthrough the fiber 204. Thus the pressure within the fluid supply isvaried to maintain the temperature at that predetermined set levelduring the hyperthermic process.

As described previously, the probe is moved to an axial location withinthe volume to be treated and the probe is rotated in steps so as to turnthe heating zone generated by the beam B into each of a plurality ofsegments within the disk or radial plane surrounding the end face 209.Within each segment of the radial plane, heat energy is supplied by thebeam B that is transmitted through the quartz capsule into the tissue atthat segment. The heat energy is dissipated from that segment both byreflection of the light energy into adjacent tissue and by conduction ofheat from the heated tissue to surrounding tissue. As stated previously,those skilled in the art will appreciate that the probe used with thecooling system in accordance with the present invention may includecircumferential fibers having point-of-source energy.

The surface of the capsule is cooled to a temperature so that it acts toextract heat from the surrounding tissue at a rate approximately equalto the dissipation or transfer of heat from the segment into thesurrounding tissue. Thus the net result of the heating effect is thatthe segment alone is heated and surrounding tissue not in the segmentrequired to be heated is maintained without any effective heatingthereon, that is no heating to a temperature which causes coagulation orwhich could otherwise interfere with the transmission of heat when itcomes time to heat that tissue in another of the segments. In this waywhen a first segment is heated to the required hyperthermic temperaturethroughout its extent from the probe to the peripheral surface of thevolume, the remaining tissues in the areas surrounding the probe areeffectively unheated so that no charring or coagulation has occurredwhich would otherwise prevent dissipation of heat and in extreme casescompletely prevent penetration of the beam B.

Thus when each segment in turn has been heated, the probe can be rotatedto the next segment or to another segment within the same radial planeand further heating can be effected of that segment only.

In practice in one example, the laser energy can be of the order of 12to 15 watts penetrating into a segment having an angle of the order of60 to 80 degrees to a depth of the order of 1.5 cm. In order to achievethis penetration without causing heating to the remaining portions ofthe tissue not in the segment, cooling of the outside of the capsule toa temperature of the order of minus 5 degrees C. is required.

In FIG. 13 is shown an actual example of a cross-section of tissue thathas been heated in three separate segments marked as sectors 1, 2 and 3.The central dark area is where the probe was located before it wasremoved to allow the cross-sectional slice to be taken. The darker areathat forms approximately 100 degrees opposite sector 2 indicates noheating has been applied to that area. The lighter color in the sectors1, 2 and 3 indicates coagulation of the tissue. Similarly it will benoted that the tissue is of the darker color (not heated) in the smallerareas between sectors 2 and 3 and between sectors 1 and 2. Thus thecooling effect of the present invention achieves the effect required oflimiting or prevention heating to the areas outside the selectedsegments.

The tube 200 is in the example shown above of a rigid structure forinsertion in a straight line as previously described into a specificlocation. The use of a rigid material such as titanium for the outertube avoids the necessity for the cannula 31 previously described andallows the alignment of the probe in its mounting and drive arrangementas previously described to the required location in the patient 13without previously setting up a cannula 31. However other arrangementscan be provided in which the tube 200 is formed of a fully or partialflexible material allowing the tube 200 to bend so as to allow insertionalong suitable passageways such as veins or arteries within the patient13 by using guiding systems well known to one skilled in the art.

Another exemplary embodiment of the invention provides a method of usinga directed energy beam in conjunction with an MRI machine to heattargeted tissue in a patient. In accordance with the aforementionedteachings, the method can be used, not only to destroy tumors, but anytissue, healthy or otherwise, that has been identified as undesirable.While the apparatus of the present invention has been described asuseable for the identification and destruction of lesions, in particulartumors, the following applications are also considered within the scopeof the present invention.

A first application pertains to treating patients having aneurysms andstokes. One object of the present invention is to treat aneurysms beforethe rupture that results in hemorrhagic stroke. Symptoms of aneurysmsare found and diagnosis is made during the “pre-event” period prior tostroke. During this period, patients are typically treated withendovascular coils. Once the aneurysm “pops” and hemorrhagic strokeoccurs, the current therapy involves clipping the ruptured vessel,usually within three days of the event. The goal is to preventrebleeding. Both procedures are risky and treatment can be much moreeasily accomplished with the probe and cooling system in accordance withthe present invention.

Strokes occur when an aneurysm in a blood vessel in the brain ruptures,causing brain damage. Aneurysms and ruptured blood vessels have longbeen treated using open brain surgery, an extremely risky procedure.Recently, a procedure known as coil embolization has gained popularitybecause it obviates the need to open the skull and expose the brain.Coil embolization involves feeding a catheter into an artery in thegroin and guiding the catheter through the arteries to the affected sitein the brain. Platinum coils are then sent up through the catheter tothe aneurysm, where the coils fill the ballooned area. The coils aredetached and left in the artery permanently, blocking the flow.

Coil embolization is not free of complications. For example, if theaneurysm opening is too wide, allowing the coils to slip out, a stent orflexible mesh tube must be inserted across the opening of the artery tohold them in place. Sometimes, surgery is still necessary if theaneurysm is not the appropriate shape for embolization. Even withoutcomplications, the procedure requires significant patience and skill tofeed a catheter from the groin into a targeted area of the brain.

The method of the present invention can be used to treat vascularlesions, such as aneurysms, and strokes and avoid many of thecomplications of coil embolization. Targeting the lesion or rupture isaccomplished in the same manner as locating a tumor. The size andlocation of the targeted lesion or rupture is determined and an optimalplacement for the cannula is chosen. Targeted vessels should be on theorder of 1 mm to 5 mm and are more preferably on the order of 2 mm to 3mm in diameter. A hole is drilled or otherwise formed in the skull andthe cannula is carefully inserted so that the cannula assumes theintended placement. A fiber assembly is inserted through the cannula inthe aforementioned manner until the target is reached. Notably, theexecution of heating the targeted area may be effected using a straightbeam rather than an angled beam if the targeted area is sufficientlysmall. Additionally, the energy source may include non-collimated lightor other form of radiant energy. It may be true that the necessarytemperature to effect the cauterization of the lesion will be lower thanthat needed to terminate tumor tissue. Alternatively, cauterization ofan lesion could be effected, according to the present invention, bythreading a more flexible, yet otherwise structurally similar, catheterthrough an artery in the groin to the targeted site. Obviously, thecatheter, or fiber assembly, would be much longer than that used withthe aforementioned cannula.

A second alternative application of the present invention is useful incosmetic surgery. The field of cosmetic surgery includes many proceduresthat remove excess healthy tissue such as skin, manipulate muscle tissueand remove fat cells, for example.

Fat cells are removed using liposuction, a procedure that involvessucking the cells through a small vacuum tube. Liposuction is arelatively violent way of removing cells and often causes damage to thecells immediately surrounding those removed. Predictably, a significantamount of fluid is also sucked through the vacuum probed during theprocedure. Fluid loss is a major concern when performing liposuction.

The probe, cooling system and method of the present invention can beused to destroy targeted fat cells by heating the cells with radiantenergy, such as collimated or non-collimated light. The fat cells areheated to a temperature just below the carbonization temperature and theremains are absorbed by the body. No fluid is removed from the body,thereby allowing a more extensive shaping procedure to be performed.Again, this procedure may be performed with a probe having an angledbeam or an axial, point-of-source energy beam.

The probe, cooling system and method in accordance with the presentinvention may also be used in cosmetic surgical procedures such asrhytidectomy, which involves the removal and redraping of excess skinand resupporting and tightening underlying muscles and tissues;blepharoplasty, which involves the removal of lax or excess kin on theupper and lower eyelids to minimize sagging; laser resurfacing to removesuperficial scars, age lines and sometimes, precancerous skin lesions;rhinoplasty, which involves the reconstruction and sculpting of the boneand cartilage to reshape the nose; and trauma reconstruction, whichinvolves the repair of facial injuries or deformities from previousinjuries. Other cosmetic surgical procedures involving the removal,repair or reconstruction of tissue are also within the scope of thepresent invention and these procedures may be performed with a probehaving an angled beam or an axial, point-of-source energy beam.

Since various modifications can be made in my invention as herein abovedescribed, and many apparently widely different embodiments of same madewithin the spirit and scope of the claims without departing from suchspirit and scope, it is intended that all matter contained in theaccompanying specification shall be interpreted as illustrative only andnot in a limiting sense.

1. (canceled)
 2. A method of in vivo hyperthermia treatment of a target tissue, the method comprising: imaging the target tissue with a magnetic resonance imaging (MRI) system; positioning a hyperthermia treatment probe in or proximate to the target tissue based on the imaging; heating the target tissue with the probe; monitoring, during the heating, changes in temperature of a volume of tissue that includes the target tissue with the MRI system to determine an amount of the heating applied to the target tissue; and terminating the heating when the amount of the heating reaches a predetermined amount.
 3. The method according to claim 2, further comprising: injecting a cooling fluid into the probe to control an amount of the heating of the probe or the target tissue.
 4. The method according to claim 3, wherein the monitoring includes monitoring changes in temperature of the volume of tissue that includes the target tissue and a portion of surrounding non-target tissue, and the injecting includes controlling an amount of cooling provided by the cooling fluid based on the monitoring.
 5. The method according to claim 2, wherein the monitoring includes monitoring changes in temperature of the volume of tissue that includes the target tissue and a portion of surrounding non-target tissue.
 6. The method according to claim 2, further comprising: after the terminating, repositioning the probe to a new position to perform heating of another target tissue based on imaging of the another target tissue.
 7. The method according to claim 2, wherein the probe includes a fiber to emit heat energy in the form of light from an external laser source.
 8. The method according to claim 7, wherein the probe includes a cooling fluid inlet and a cooling fluid outlet, and the method further comprises: injecting, during the monitoring, a cooling fluid into the cooling fluid inlet to control and limit an amount of the heating of the probe or the target tissue; and outputting the cooling fluid from the cooling fluid outlet.
 9. The method according to claim 8, wherein the injecting the cooling fluid causes the cooling fluid to contact a heat energy-emitting portion of the fiber.
 10. The method according to claim 9, wherein the probe has a longitudinal axis and the probe is to emit heat energy in the form of light in a limited angular region in a direction that is substantially lateral to the longitudinal axis.
 11. The method according to claim 8, further comprising: controlling a flow of the cooling fluid based on the monitoring; and controlling the external laser source to control an amount of heat energy emitted from the probe during the monitoring.
 12. A hyperthermia treatment system to provide in vivo hyperthermia treatment of a target tissue, the system comprising: a magnetic resonance imaging (MRI) system to image the target tissue and to monitor, during an in vivo hyperthermia treatment of the target tissue, changes in temperature of a volume of tissue that includes the target tissue to determine an amount of the heating applied to the target tissue; and a probe to apply the in vivo hyperthermia treatment of the target tissue, the probe including: a housing, a fiber provided in the housing to emit heat energy in the form of light from an external laser source to the target tissue, a heat energy-emitting portion of the fiber provided in a space within the housing, a cooling fluid inlet to input a cooling fluid to the space in the housing, and a cooling fluid outlet to output the cooling fluid from the space in the housing.
 13. The system according to claim 12, wherein the cooling fluid inlet is to cause the cooling fluid to contact the heat energy-emitting portion of the fiber in the space in the housing.
 14. The system according to claim 13, wherein the probe has a longitudinal axis and the probe is to emit heat energy in the form of light in a limited angular region in a direction that is lateral to the longitudinal axis.
 15. The system according to claim 12, further comprising: a controller to control an amount of heating emitted by the fiber and an amount of cooling provided by the cooling fluid based on temperature monitoring of the volume of tissue by the MRI system, during the temperature monitoring by the MRI system.
 16. The system according to claim 15, wherein the MRI system is to image the probe during the in vivo hyperthermia treatment to provide a positioning relationship between the probe and the target tissue, and the controller is to control the amount of heating and the amount of cooling based on the positioning relationship. 